1. Field of the Invention
The invention relates to field emission flat panel displays, and more particularly to methods for making a high resolution matrix addressed flat panel display having single field emission microtip redundancy with resistive base and the resulting display.
2. Description of the Related Art
U.S. Pat. No. 4,763,187 to J. P. Biberian generally discusses field emission device structures including tips emitting electrons to light a fluorescent screen, using lines and columns for addressing. The structure includes a grid, at a third voltage potential (the first two potentials being those of the cathode and anode) which is used to control electron emission intensity. Biberian says that the grid solves the problem of needing low voltage levels (to allow for fast switching) but without requiring very small spacing, on the order of a few microns, between the tips and the anode structure. A few micron spacing would cause great difficulty in manufacturing. His structure using the grid also allows for the separate control of the address and intensity functions.
Another matrix addressed flat panel display is shown in U.S. Pat. No. 4,857,799 by C. A. Spindt et al. He refers to U.S. Pat. No. 3,500,102 by Crost et al which deals with a thin display using field emission, but which did not deal with gaseous breakdown, and which would still have a problem of distortion in the display picture, due to screen deflection from pressure difference between atmospheric pressure and vacuum inside display. Solutions to this problem proposed by Spindt et al included: 1) a "support structure" to prevent the distortion, 2) spacing between the cathodes and luminescent material which is less than or equal to the mean free path of electrons in the interelectrode space--this would help reduce gas breakdown, and 3) isolating the cathode conductive lines by using semiconductive material between the conductive lines, to reduce cross-talk.
The U.S. Pat. No. 4,857,161 to Borel et al shows a process for the production of an array of cathode lines and grid lines that are used to address each picture element. At each picture element there are many micro-emitters that are grown on the corresponding cathode line. The many micro-emitters provide redundancy, so that if one emitter fails, there is no degradation in the display.
The U.S. Pat. No. 4,940,916 to Borel et al addresses two problems with the Borel et al U.S. Pat. No. 4,857,161, that is cathode destruction and non-uniform emission or "bright spots" on the display. During startup of the display, current surges due to degasification occur, including arcing between the grids, points and anodes, leading to cathode destruction (the cathode is unable to carry current and opens). Initially a resistor was added between the power source and the cathode lines, but under certain conditions this led to the bright spots problem. His solution was to add a resistive layer covering the cathode layer and under the microtips. His purpose is to prevent cathode destruction and offer good thermal dissipation.
The resistive layer approach described by Borel et al still has the problem that it cannot sustain cathode-gate voltage, and subsequent explosions cause a dead short between the gate and cathode. A solution for this is proposed by A. Meyer in "RECENT DEVELOPMENT ON `MICROTIPS` DISPLAY AT LETI" in TECHNICAL DIGEST of IVMC 91 NAGAHAMA 1991 PAGES 6 to 9. The solution is to form a meshed conductor of the cathode lines. This has the effect of moving the cathode farther from the emitters for a longer resistive path. The conductor mesh also provides additional redundancy.
However, the meshed conductor of Meyer has less value as the display resolution is increased and/or a smaller pixel size is desired. Therefore, the resolution is unsatisfactory for the pixel sizes needed today.
Spindt in U.S. Pat. No. 3,789,471 discusses generally the formation of field emission cathode structures, and in one embodiment the formation of a pedestal for forming an emitter tip thereon.